In situations where the speed of a motor must be continually monitored, the prior art has provided for many forms of speed measurement, and also for the direction of rotation of the motor shaft. Optical methods have been demonstrated as well as magnetic devices. One such teaching of magnetically sensed rotational velocity of a motor can be found in U.S. Pat. No. 4,488,076, to Donald J. Macleod, which issued on Dec. 11, 1984. This patent discloses the use of a commutator magnet portion which rotates with the shaft of the motor. The stator portion includes conducting traces which are situated such that the rotation of the commutating magnet past the traces on the circuit board induces a current in the traces. However, this patent does not teach the accuracy of a multi-phase tachometer or the use thereof for accurate rotational speed determination and the direction of rotation.
According to a first embodiment of the present invention, a multi "winding", multi-phase PCB tachometer that uses a single multi-pole magnet is constructed by using double sided boards with plated through holes. The radial elements of two or more "windings" can be interlaced with equal spacing, then the ends of the respective elements linked together with PCB trace crossover being accomplished on the back side of the PCB. That is, the radial arms of the traces would all be on one side of the PCB. The outer edges or circumferential elements thereof would be formed as traces on the other side of the board and connected by the many plated through holes 48. In a second embodiment, a multi-phase tachometer configuration is disclosed in which the number of radial printed circuit traces and the number of pole magnets are not equal, whereby the individual voltages generated across each radial segment will not be in phase, and thus can provide rotational direction information as well as velocity information. Increased resolution is also provided. The printed circuit traces are closed loop, rather than open circuited, and provide for accurate speed and direction information.